1. Field of the Invention
Embodiments described herein relate generally to an RF (radio frequency) coil device and a magnetic resonance imaging apparatus.
2. Description of the Related Art
MRI is an imaging method which magnetically excites nuclear spins of an object set in a static magnetic field with an RF signal having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation. The aforementioned MRI means magnetic resonance imaging, the RF signal means a radio frequency signal, and the MR signal means a nuclear magnetic resonance signal.
Here, the device, that fulfills the role of transmitting an RF signal to a nuclear spin by supplying RF pulse current to a coil and the like and receiving a generated echo signal as an MR signal, is an RF coil device (for example, refer to the after-mentioned Patent Document 1 and Patent Document 2). The RF coil devices are classified into a whole body type and a local type. Various types of the RF coil devices for a local area are used according to an imaging part. For example, in the case of imaging of a shoulder joint, a dedicated RF coil device for a shoulder joint is set to the shoulder of an object.    [Patent Document 1] Japanese Patent Application Laid-open (KOKAI) Publication No. 2007-229004    [Patent Document 2] Japanese Patent Application Laid-open (KOKAI) Publication No. 2001-95776
Conventional RF coil devices for a shoulder joint are dented like a bowl so that they cover over and fit on the shoulder under the pose in which the arm of an object is down. However, for example, in the case of imaging of a shoulder joint after administration of contrast medium, imaging under the pose in which the arm of an object is raised is sometimes desired. In this case, there is airspace between the conventional RF coil device and the shoulder due to the dent, the shoulder is separated from the RF coil device by the space corresponding to the airspace, and signal intensity of received nuclear magnetic signals becomes weak.
On the other hand, if different RF coil devices are respectively set for imaging under the pose in which the arm is raised and imaging under the pose in which the arm is down, this results in an increase in cost.
Thus, a configuration, in which one RF coil device can meet both of imaging under the pose in which the arm is raised and imaging under the pose in which the arm is down, is preferable.
Therefore, as an RF coil device for a shoulder joint in MRI, technology to enable the RF coil device to be effortlessly set on the shoulder under both poses with the arm raised and down, as well as keep sufficient coil sensitivity has been desired.